A Warrnambool man who believes he is the king of Australia and Norway has been jailed for three years and two months for viciously assaulting police officers who asked a teenager to wear a mask during one of Victoria's COVID-19 lockdowns.

Steven John Cleary pleaded guilty to several charges in the County Court, including assaulting an emergency worker on duty and intentionally causing injury.

Police body camera footage captured the entire incident, showing police officers Senior Constable Rowan Baldam and Constable William Ringin attempting to stop a 15-year-old in Warrnambool who was not wearing a mask.

During sentencing today, Judge Anne Hassan said Cleary's offending could only be explained by his mental impairment. 

"Your paranoia and delusional thinking ran rampant during COVID-19," she said.

The court heard the 50-year-old experienced delusions, including that he was the king of Australia and Norway and that COVID was a conspiracy.

Cleary refuses to take medication for his illness.

His sentence includes a non-parole period of one year and 10 months.

He has spent 287 days in pre-sentence detention.

'Deeply concerned'

Police Association of Victoria chief executive Wayne Gatt described the sentence as "disappointing".

"In all my time in policing, this is one of the most serious premeditated assaults that I've seen on police officers in uniform," he said.

"The word 'shocking' doesn't accurately describe the degree of that assault.

"That would be at the top end … the extreme top end.

Mr Gatt acknowledged Cleary's mental impairment but said the sentence sent a concerning message to all emergency service workers.

"If mental health continues to be this supposed free kick, it's disproportionate, we think," he said.

Mr Gatt said his comments were not a direct criticism of Judge Hassan, but of "the system".

"She has had a very difficult decision to make, but the system hampers her," he said.

'This is an act of war'

The incident took place on October 9, 2021, when mask-wearing was mandated by the state government.

Despite repeated requests from police to explain why he was not wearing a mask, the boy refused to share his personal details and contacted Cleary via a walkie-talkie.

Cleary arrived at the scene armed with a metal baseball bat and approached the two officers.

Senior Constable Baldam repeatedly told the 50-year-old he would be tasered if he did not back off, but Cleary refused to stop and rushed forward in what Judge Hassan described as an "eruption of violence".

The footage showed Cleary repeatedly striking Senior Constable Baldam in the head, causing him to fall to the ground.

Despite Senior Constable Baldam screaming and groaning in pain in the fetal position with blood pouring out of his head, Cleary continued to hit the officer on the ground with the bat.

Constable Ringin managed to grab the bat from the attacker's hands, despite being repeatedly punched by the teen.

The accused picked up one of the officers' tasers, which had been dropped on the ground during the fracas, and shot it at Constable Ringin, who managed to strike Cleary at the same time, causing him to fall to the ground.

Senior Constable Baldam managed to get back up on his feet and assist his partner with restraining Cleary.

The 50-year-old repeatedly refused orders from the officers, telling them several times, "I am king".

"You are a Roman dog, this is an act of war," Cleary told the officers.

'Worst day of my life'

Both victims repeatedly broke down while reading their victim impact statements to the court on Wednesday.

Senior Constable Baldam said he thought he was going to die during the incident.

"I wondered if this injury would be survivable," he said.

The officer said doctors told him he was "lucky" to not have a brain injury.

Senior Constable Baldam said he continued to suffer recurring pain from his fractured left thumb and had a permanent scar on his head as a result of the "unprovoked, absurd attack".

"Being assaulted has stunted my careers and earnings," he said.

"Steven clearly is responsible for my physical injuries … but far more significantly, he has altered the trajectory of my life forever."

Constable Ringin also detailed the dramatic, negative impacts Cleary's actions have had on many aspects of his life.

"My family has pleaded for me to consider a career change," Constable Ringin said.

"This breaks my heart … it's been my dream since childhood.

"Work is now the greatest reminder of the worst day of my life."